Boron dipyrromethenes, commonly known as BODIPY, form one of the most popular groups of organic flurophores, attracting interest from applications due to their high emission yields, photostability and versatile chemistry. The organic part of the BODIPY molecule is dipyrromethene (dipyrrin), which is responsible for the strongly allowed π-π* transition in the visible region of the spectrum. Coordination with boron rigidifies the dipyrrin skeleton, resulting in yet more intense absorption and bright fluorescence.
However, unlike BODIPY, the majority of metallodipyrrins do not fluoresce. Moreover, the interplay between the structure and the photophysical properties of metallodipyrrins has not yet been fully established, and overall metallodipyrrins are presently considered poorly emissive species.
The synthesis of dipyrrin compounds has been described, for example, by Maekawa et al., Chemische Berichte, 101, 847, 1968 and Shen et al., Chemistry, A European Journal, 10, 4853-4871, 2004. However, these processes suffer from certain drawbacks, such as lack of substitution capabilities, and/or low functional group tolerance.
Thus, there remains a need in the art for new highly emissive metallodipyrrin complexes that may be useful in, e.g., sensing, imaging and laser applications. Moreover, there also remains a need in the art for new processes for the synthesis of fluorogenic dipyrrin chelators that afford such compounds in improved yields and/or purities and is amenable to the introduction of a wide range of functional group substituents.